Polypropylene terephthalate twisted yarn and method for producing the same

ABSTRACT

The present invention offers polypropylene terephthalate textured yarn which has little dyeing unevenness or fibrillation, and is outstanding in its product quality, by carrying out texturing at the same time as drawing under specified conditions using polypropylene undrawn yarn; together with a method for the production thereof.

TECHNICAL FIELD

The present invention relates to polypropylene terephthalate texturedyarn which, while making the most of the softness and stretchability ofpolypropylene terephthalate, can effectively confer bulkiness and asense of tightness when in the form of a fabric such as a woven orknitted material; and to an industrially outstanding method for theproduction thereof.

PRIOR ART

As polyester textured yarn, textured yarn comprising polyethyleneterephthalate is outstanding in its crimp characteristics,weatherability and the like, and it is currently widely used. However,there is a need to further enhance the comfort in wearing, and a fibreof high stretchability is demanded. Thus, as described in JP-A-9-78373and JP-A-11-93026, textured yarns employing polypropylene terephthalatehave been proposed. These textured yarns are textured yarns withoutstanding stretchability and bulkiness, having an elastic recovery ofat least 80% at the time of 50% elongation, a crimp development factorof 200-300% and a crimp recovery of 80%. However, in the case of thesetextured yarns, drawn yarn is subjected to so-called spindle texturingand the processing rate is slow, being at most 100 m/min, and not onlyare production costs high but there is also considerable variationbetween spindles and within a spindle, and there are problems in termsof quality. Furthermore, because of the low Young's modulus of no morethan 30 g/d, there are problems in applying tightness.

OBJECTIVE OF THE PRESENT INVENTION

The objective of the present invention is to provide a method for theproduction of textured yarn of high quality and at low cost frompolypropylene terephthalate which is outstanding in its stretchabilityand bulkiness; together with polypropylene terephthalate textured yarnwhich, in terms of its handle, is outstanding in its sense of tightness.

DISCLOSURE OF THE INVENTION

The method of the present invention for producing polypropyleneterephthalate textured yarn which meets the aforesaid objective ischaracterized in that, when carrying out texturing at the same time asdrawing using a frictional false-twisting machine, at the same time assetting the draw ratio of the polypropylene terephthalate undrawn yarnto 1.05-1.70, the elongation EL (%) of the undrawn yarn and the drawratio DR are set so that the following relationship (1) is satisfied.

0.585×(1+EL/100)≦DR≦0.75×(1+EL/100)  Realtionship (1)

Furthermore, the polypropylene terephthalate textured yarn of thepresent invention is characterized in that it is produced by the abovemethod.

BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1: This shows the stress-strain curve when polypropyleneterephthalate drawn yarn was stretched with the atmospheric temperaturevaried from room temperature (25° C.) to 170° C.

FIG. 2: This is a schematic diagram for explaining one example of thefalse-twisting machine relating to the present invention.

FIG. 3: This is a process diagram showing an example of the spinningequipment for obtaining highly-oriented undrawn yarn.

FIG. 4: This is a process diagram showing an example of spinningequipment where a hot roll has been incorporated as the second godetroll.

FIG. 5: This is a process diagram showing an example of spinningequipment where a non-contact heater is incorporated on the spinningline.

FIG. 6: This is a model diagram for explaining the saddle and thebulging factor in the case of the undrawn yarn package preferably usedin the present invention.

EXPLANATION OF THE NUMERICAL CODES

1: undrawn yarn package

2: 1^(st) FR

3: heater

4: cooling plate

5: frictional false-twisting device

6: 2^(nd) FR

7: 3^(rd) FR

8: entangling nozzle

9: 4^(th) PR

10: winder

11, 18: spinning block

12, 19: oiling means

13, 20: undrawn yarn

14, 21: entangling nozzle

15, 22: first godet roll

16, 23: second godet roll

17, 24: winder

25: separating roll

26: spinneret

27: chimney

28, 32: non-contact heater

29: oiling means

30: entangling nozzle

31: first godet roll

33: second godet roll

34: winder

PRACTICAL FORM OF THE INVENTION

In the method of producing the polypropylene terephthalate textured yarnof the present invention, when carrying out the texturing at the sametime as drawing using a frictional draw-texturing machine, at the sametime as setting the draw ratio of the polypropylene terephthalateundrawn yarn to 1.05-1.70, the elongation EL (%) of the undrawn yarn andthe draw ratio DR are set so that the following relationship (1) issatisfied.

0.585×(1+EL/100)≦DR≦0.75×(1+EL/100)  Relationship (1)

Here, the polypropylene terephthalate (abbreviated below to PPT) of thepresent invention is a polyester obtained from an acid component chieflycomprising terephthalic acid and a glycol component chiefly comprising1,3-propanediol. However, it may also include other copolymer componentswhich can form other ester linkages in a proportion not exceeding 20 mol% and more preferably not exceeding 10 mol %.

Examples of copolymerizable compounds are dicarboxylic acids such asisophthalic acid, succinic acid, cyclohexanedicarboxylic acid, adipicacid, dimer acid and sebacic acid, and glycol components such asethylene glycol, diethylene glycol, butanediol, neopentyl glycol,cyclohexanedimethanol, polyethylene glycol and polypropylene glycol, butthere is no restriction to these.

Furthermore, optionally, there may be added titanium dioxide as adelustring agent, fine particles of silica or alumina as a lubricant, ahindered phenol derivative as an antioxidant, or colouring pigments andthe like.

The undrawn yarn comprising PPT is preferably fibre having a breakingelongation of from 60% to 180%. Such undrawn yarn is obtained forexample using a normal spinning machine, with the PPT being melted inthe usual manner and led into the spinning pack, and spinning carriedout from the spinneret at a spinning rate of 2500 to 4500 m/min. Thestrength of the undrawn yarn obtained at a spinning rate of less than2500 m/min is low, so considerable yarn breakage occurs in the drawtexturing. Furthermore, undrawn yarn wound up at a spinning rate of1000-2500 m/min displays marked change with elapse of time, sodifferences in fibre structure are produced between the centre and edge,and the inner and outside layers, of the undrawn package, resulting inproblems such as uneven dyeing of the draw textured yarn in the yarnlengthwise direction occurring.

Again, in carrying out texturing at the same time as drawing at a drawratio in the range from 1.05 to 1.70, it is preferred that there beemployed a false-twisting machine comprising in turn a first feed roller(1^(st) FR), a heater, a cooling plate, the frictional false-twistingdevice and a 2^(nd) feed roller (2nd FR), with drawing being carried outby a factor of 1.05 to 1.70 between the 1^(st) FR and the 2^(nd) FR,upstream twisting being effected by the frictional false-twistingdevice, heat-setting being conducted by means of the heater and fixingof the state being performed by means of the cooling plate. Again, forthe purposes of obtaining thick/thin textured yarn where the thicknessvaries in the fibre axial direction, there may be carried outpreliminary drawing within a range that does not exceed the natural drawratio of the undrawn yarn, after which, without temporarily winding-up,the yarn is directly treated in the manner described above, with twistbeing applied upstream of the frictional false-twisting device usingsaid frictional false-twisting device while drawing between the 1^(st)FR and 2^(nd) FR, and heat-setting being conducted by means of theheater and fixing of the state being performed by means of the coolingplate. However, in such circumstances, taking the draw ratio prior tothe 1^(st) FR as DR₀ and the draw ratio between the 1^(st) FR and the2^(nd) FR as DR₁, the value of DR obtained by multiplying thesetogether, that is to say DR=DR₀×DR₁, will be from 1.05 to 1.70. Now, thepreferred draw ratio range is 1.05 to 1.60, with the range 1.10 to 1.50still further preferred.

Again, in the present invention, the elongation EL (%) of the undrawnyarn and the draw ratio DR in the draw-texturing are set such that thefollowing relationship (1) is satisfied.

0.585×(1+EL/100)≦DR≦0.75×(1+EL/100)  Relationship (1)

When the draw ratio DR is less than 0.585×(1+EL/100), ballooning occursduring the draw-texturing process, processing becomes unstable and thereare many yarn breaks. Moreover, if the elongation of the textured yarnexceeds 60%, when made into cloth there are problems in terms of productquality such as bagginess at the elbows. On the other hand, if the DRexceeds 0.75×(1+EL/100), the processing tension becomes too great,filament fibrillation occurs and, furthermore, there is considerableyarn breakage, and so this is undesirable. The specific draw ratioshould be set in accordance with the properties of the polypropyleneterephthalate undrawn yarn and the textured yarn, but it is preferredthat it be such that the residual elongation is 20-60%, more preferably25-55% and in particular 30-50%.

In order to enhance the stretchability and bulkiness of the cloth, it isnecessary to enhance the crimp characteristics of the textured yarn, andto achieve this it is preferred that, in the draw texturing process, theyarn temperature at the heater outlet be made 30-175° C. Furthermore, inorder to produce the cross-sectional deformations for providing thetextured yarn with tightness, it is more preferred that the yarntemperature at the heater outlet be made 100-175° C. 110-160°0C. isstill further preferred.

It has been newly discovered that if the stress-strain curve is measuredwhile heating PPT, then, as shown in FIG. 1, the elongation and thestrength are both markedly lowered by the heating. This is a phenomenonnot found with polyethylene terephthalate or the like, and was regardedas a major problem for draw-texturing where drawing is carried out whileheating. However, as a result of considerable research, it has beendiscovered that a texturing tension T₁ of 0.17 to 0.55 cN/dtex enablesthe texturing process to be carried out stably. When the texturingtension T₁ is in the range 0.17 to 0.55 cN/dtex, ballooning does notreadily occur and fibrillation or yarn breaks do not tend to arise, sohigh-speed processing is possible. Furthermore, for the same reasons, itis further preferred that the texturing tension T₁ be in the range from0.25 to 0.40 cN/dtex. Here, the texturing tension T₁ denotes the tensionjust prior to the frictional false-twisting device.

The Young's modulus of PPT is low, so there tends to be lower twistpropagation upstream when compared to polyethylene terephthalate. Inparticular, if the yarn is not twisted over the heater positioned at thefurthest point upstream, the fall in tension in the heater isconsiderable and, not only are the crimp characteristics lowered, butalso there is considerable filament fibrillation and yarn breaks.Consequently, it is preferred that the ratio T₁/T_(H) of the texturingtension T₁ to the tension prior to the heater T_(H) be from 1.02 to1.30. When the ratio T₁/T_(H) of the texturing tension T₁ to the tensionprior to the heater T_(H) is in the range 1.02 to 1.30, there is littledrop in tension within the heater, that is to say the twist from thefrictional false-twisting device is fully manifested over the heater,and filament fibrillation and yarn breaks do not readily occur, so thisis preferred. More preferably T₁/T_(H) is 1.02 to 1.25. Here, thetension prior to the heater is the tension immediately before enteringthe heater.

The number of twists T inside the heater is preferably as high aspossible but there are problems in the twist-conferring capacity of africtional false-twisting device and, specifically, the number of twistsT inside the heater is preferably from 27400/D^(½) to 30600/D^(½). Inthis way, it is possible to prevent fibrillation and yarn breaks insidethe heater. For the same reasons, it is more preferred that the numberof twists inside the heater is from 27900/D^(½) to 30100/D^(½). Ddenotes the fineness (decitex) of the textured yarn which has undergonethe draw-texturing process.

Next, using the drawings, explanation is given of the method ofproducing the PPT textured yarn of the present invention. An example offalse twisting equipment relating to the present invention is shown inFIG. 2.

Using PPT undrawn yarn as the supplied raw yarn, while drawing iscarried out between 1^(st) FR 2 and 2^(nd) FR 6, in the state with twistapplied using frictional false-twisting device 5 the twisted form isheat-set by means of heater 3, and the form then fixed by means ofcooling plate 4.

As stated earlier, since the Young's modulus of PPT is low, thepropagation of the false twist upstream tends to be lowered, and so itis important in the twist zone to avoid ore than the required yarnbending and contact resistance.

Consequently, it is important that all the parts employed in thefalse-twisting machine be selected from the viewpoint of lowering thecontact resistance. With regard to heater 3, there can be employedpassage over a metal plate heated by means of an electrical heater or byheating and circulation of a heating medium, or there can be used themethod of passage through a high temperature atmosphere. In the case ofpassage over a heated metal plate, it is preferred that this not belonger or bent more than is necessary, taking into account the yarnfineness, the processing rate and the desired texturing temperature.Furthermore, in the case of passage through a high temperatureatmosphere, in order to raise the transit stability, it is preferredthat there be used a so-called non-contact type high temperature heaterwith the yarn pathway fixed by guides or the like. In order to reducefibrillation and breakage of the textured yarn, and in order to raisethe processing rate, the use of a non-contact type high temperatureheater of lower contact resistance is further preferred.

It is also preferred that the cooling plate 4 be no longer thannecessary, and it is preferred that the cooling plate be shortened bycooling said cooling plate by the circulation of cooling water, or thatthe yarn be cooled at the same time as fumes are extracted by sucking-inair. Furthermore, with a cooling plate where slits are produced by meansof metal plates and suction is applied from the rear so that the yarn iscooled by means of a cross-flow, the processing can be conducted stablywith the frictional resistance lowered, the cooling capacity raised andthe twist zone shortened, so this is preferably employed.

With regard to the frictional false-twisting device 5, providing it hasboth a twist-conferring action and a feeding action, it may be either aninterior-contact type or exterior-contact type frictional false-twistingdevice, but there is preferably employed an exterior-contact typetriaxial twister or belt nip twister.

The PPT undrawn yarn used as the supplied raw yarn tends to show delayedshrinkage following melt spinning and winding-up. In particular, undrawnyarn which has been wound-up at a spinning rate of 1000-2000 m/min showsa marked change in properties with elapse of time, so that differencesin shrinkage arise between the edge face and centre of the package, orbetween the inner and outer layers, and lengthwise direction dyeingunevenness is produced in the draw-textured yarn. However, even atspinning rates in the region of 3000 m/min, delayed shrinkage is stillproduced and this causes yarn lengthwise dyeing unevenness to arise.Moreover, if the spinning rate is increased in order to reduce thedelayed shrinkage, there is a higher degree of molecular orientation inthe spinning line, so that the phenomenon of package tightening isproduced with the result that it is no longer possible to remove thepaper tube from the spindle. Hence, in order to resolve this problem, itis preferred that there be used, as the supplied raw yarn, undrawn PPTwhich satisfies the following four relationships (1) to (4).

(1) strength ST (cN/dtex): 1.8≦ST

(2) birefringence Δn (×10⁻³): 30≦Δn≦70

(3) elongation EL (%): 60≦EL≦180

(4) boiling water shrinkage SW (%): 3≦SW≦15

In other words, with undrawn yarn showing these properties, there ispractically no tightening of the undrawn yarn package due to delayedshrinkage and, as well as showing good texturing process properties,there are few defects such as dyeing unevenness, and a high qualitytextured yarn is produced.

The strength has a considerable influence on the process transitcharacteristics when carrying out drawing, false-twisting, warping andweaving, and on the mechanical properties of the cloth. In order to besatisfactory in terms of the productivity and product quality asaforesaid, it is preferred that the strength be at least 1.8 cN/dtex andmore preferably at least 2.2 cN/dtex.

Again, in order to improve the processing characteristics in the drawingand texturing stage, it is preferred that the elongation be at least60%. In terms of reducing unevenness in the thickness of the yarnobtained by drawing and false-twisting, to produce a more uniform yarn,it is preferred that the elongation be no more than 180%. The elongationrange 70 to 150% is further preferred.

Moreover, the birefringence is closely related to the mechanicalproperties of the undrawn yarn and, in particular, in order to preventfibrillation and breaks in the false-twisting process stage, and inorder to obtain good process transit characteristics, it is preferredthat the birefringence be at least 0.03. Furthermore, if thebirefringence, exceeds 0.07, it becomes difficult to fully suppresspackage tightening or delayed shrinkage at high temperature. A morepreferred range for the birefringence is 0.04 to 0.065.

Again, when PPT fibre is unwound from an undrawn yarn package andreleased from stress, it slowly shrinks, and a phenomenon referred to asdelayed shrinkage is produced. This phenomenon also slowly proceedswithin the package, and various problems arise such as the package shapebeing destroyed, unwinding being difficult, and unevenness beingproduced in the thickness of the yarn matching the package edge faceperiod. Furthermore, this delayed shrinkage tends to be governed by theenvironmental temperature of the undrawn yarn and, in particular, sincethe environmental temperature reaches 50° C. in the case of summertimetruck deliveries, the extent of the delayed shrinkage can beconsiderable. Hence, it is important that the fibre structure of theundrawn yarn be heat-stabilized at the yarn production stage. Thestability of the fibre structure to heat can be ascertained from itsboiling water shrinkage by introducing a sample into boiling water andmeasuring the shrinkage. If the boiling water shrinkage is less than15%, there is little change with passage of time due to delayedshrinkage and the yarn can be said to have excellent heat stability.Furthermore, the boiling water shrinkage is closely related to the crimpsetting property in the false-twisting process and with a percentageshrinkage of at least 3% excellent crimp setting is shown, The boilingwater shrinkage is more preferably 5 to 12%.

Moreover, by having a low value of Uster unevenness, which is an indexof the yarn thickness unevenness in the undrawn yarn lengthwisedirection, not only is it possible to raise the process stability bysuppressing fluctuations in the processing tension in the false-twistingprocess, but it is also possible to reduce defects such as dyeingunevenness in cloth derived from the yarn obtained, and it is possibleto produce high quality products. Consequently, the Uster unevennessvalue of the undrawn yarn used is preferably no more than 1% and morepreferably no more than 0.8%.

The undrawn yarn used is preferably wound into a cheese-shaped package.The shape of the package has an influence on the unwinding properties ofthe yarn in the false-twisting process, so a good package shape isrequired. Normally, where package shape is a problem is in terms ofsaddle and bulging, and if both these are small then the package isexcellent in its high speed unwinding properties. In accordance with themethod conceived by the present inventors, the fibre internal structureis stabilized prior to winding-up as a package, and so it is possible toproduce a cheese of good package shape. The rate of unwinding requiredin false-twisting reaches 200-800 m/min, and in order that there belittle variation in the unwinding tension at such rates and in orderthat yarn processing be carried out stably, it is preferred that thesaddle be less than 4 mm and the bulging factor be less than 10%. Morepreferably, the saddle is less than 3 mm and the bulging factor is lessthan 7%. Now, the saddle and the bulging factor are measured using a 4kg wound package.

Next, an example of the undrawn yarn production method preferablyemployed in the present invention is provided. Known methods can be usedas they are for the production of the PPT which forms the chief startingmaterial for the undrawn yarn. The intrinsic viscosity [η] of the PPTused is preferably at least 0.75 and more preferably at least 0.85 inorder to enhance the fibre-forming properties at the time of spinningand in order to obtain yarn of practical strength. The oligomer chieflycomprising cyclic dimer which is present in the PPT starting materialcontaminates the spinneret at the time of spinning and promotes thedeposition of needle crystals in the housing below the spinneret, andhas an adverse effect on the yarn production properties, so the oligomercontent should be made as low as possible, preferably no more than 2 wt%, more preferably no more than 1.5 wt % and still more preferably nomore than 1 wt %. Solid phase polymerization is an effective means forreducing the amount of the oligomer. After producing PTT of intrinsicviscosity [η] 0.4 to 0.7 by means of liquid phase polymerization, solidphase polymerization can be carried out at a temperature of 180-215° C.,for an exposure time of 2 to 20 hours, under nitrogen, argon or otherinert gas, or under a reduced pressure of degree of vacuum below 10torr, and more preferably below 1 torr. Again, thebis(3-hydroxypropyl)ether produced at the time of polymerization has atendency to reduce the softening point or lower mechanical propertiessuch as the strength, so the content thereof should be as low aspossible, preferably no more than 2 wt %, more preferably no more than 1wt % and still more preferably no more than 0.5 wt %.

The PPT undrawn yarn can be produced by uninterrupted polymerization andspinning, in which the spinning is performed directly after thepolymerization, or chip may first be produced, then this dried orsubjected to solid phase polymerization, after which the spinning isperformed. However, in order to reduce the oligomer content as describedabove, it is preferred that chip first be produced and that solid phasepolymerization be carried out.

The method of producing the undrawn yarn preferably employed infalse-twisting according to the present invention is now explained withreference to the drawings.

With regard to the spinning temperature when carrying out the meltspinning, in order to achieve stable discharge at the spinneret thespinning is preferably carried out at a temperature 15-60° C. higherthan the melting point of the PPT, and more preferably it is carried outat a temperature 25-50° C. higher. Again, in order to suppress oligomerdeposition during spinning and to enhance the spinning properties,optionally there may be provided under the spinneret a 2-20 cm heatingtube or MO (monomer, oligomer) suction means, or a device for generatingan inactive gas such as air, steam or N₂ for preventing oxidativedegradation of the polymer and contamination of the spinneret.

The spinning rate should be set such that, as described above, thestrength of the undrawn yarn is at least 1.8 cN/dtex and the residualelongation is 60-180%, and for this purpose the spinning rate ispreferably in the range 2500 to 4500 m/min. Again, after spinning, thefibre properties can be stabilized by heat treatment under specifiedconditions prior to winding-up.

If the spinning rate is less than 2500 m/min, the birefringence will below, at less than 0.030, so the strength is reduced, and fibrillationand filament wrap-around will tend to arise at the time offalse-twisting. If it exceeds 4500 m/min, the yarn will have a so-calleddrawn yarn structure and will be difficult to deform, so that as well asthe crimp characteristics following false-twisting being reduced, thereis also a tendency for fibrillation and wrap-around of filaments tooccur.

Again, following spinning, it is important that a heat treatment becarried out under specified conditions prior to winding-up, and bycarrying out said heat treatment continuously, prior to winding-up,there is achieved a stabilized fibre structure. Changes which occur withpassage of time following winding-up are suppressed and it is possibleto avoid edge face period unevenness, and differences between the innerand outer layers. For example, in the spinning equipment shown in FIG.4, the PPT is melted, discharged from spinneret 18 and, while beinghauled off using 1^(st) godet roll 22, a heat-treatment is carried outby means of heated 1^(st) godet roll 22 or 2^(nd) godet roll 23, andthen winding-up is performed using winding machine 24. Now, theheat-treatment time will depend on the heat-treatment temperature, butfrom 0.01 to 0.1 second is required so it is preferred that the yarn bepassed around heated godet roll 23 a number of times using separatingroll 25. A further-preferred heat-treatment time is 0.02 to 0.08seconds. Moreover, heat treatment is not restricted to the use of theaforesaid heated godet roll and, as shown in FIG. 5, a non-contactheater employing hot air or steam as a heating medium may be provided onthe spinning line (between the spinneret and the 1^(st) godet roll) orbetween the godet rolls.

The heat-treatment temperature in the case of a contact-type heater suchas a godet roll is preferably 70-130° C. and in the case of anon-contact heater it is preferably 120-220° C. More preferably, for acontact heater it is 100-125° C. and for a non-contact heater it is140-200° C. Furthermore, it is possible to improve the effectiveness interms of suppressing package tightening and delayed shrinkage by meansof a relaxation treatment following hauling-off by the 1^(st) godet roll22, between the 2^(nd) godet roll 23 and the winding machine 24, so thisis preferred.

The textured yarn which has been produced and wound-up by the abovemethod may still show package tightening due to delayed shrinkage. Insuch circumstances, as well as the unwinding properties of the texturedyarn being impaired, dyeing unevenness arises in the yarn lengthwisedirection as a result of change with passage of time. In order toprevent this, it is preferred that, following the texturing process, theyarn be introduced into a relaxation stage, and it is preferred that arelaxation zone for 5 to 25% relaxation to occur in the room temperaturestate be provided after the draw texturing and prior to winding-up.Specifically, in FIG. 2 for example, this can readily be realized byslowing the surface velocity of the 3^(rd) FR in terms of 2^(nd) FR 6.In the relaxation zone, there need not necessarily be carried out heattreatment by means of a heating device, and it is possible to preventpackage tightening at room temperature.

Textured yarn which has been obtained by the processing of PPT drawnyarn using a spindle false-twisting device shows considerable variationbetween spindles, the pass rate in the knitting inspection is about 93%at best, and a considerable cost in entailed in the inspection stage. Onthe other hand, with the textured yarn produced by the production methodof the present invention, it is possible to achieve a knittinginspection pass rate of at least 95%, so that a simplification of theinspection stage is possible, and hence his is preferred. Again, byfully providing the required equipment, it is possible to achieve aknitting inspection pass rate of at least 98%, so it is possible toeliminate the inspection stage, and therefore this is still furtherpreferred.

In addition, in the case of spindle false-twisting which is carried outusing drawn yarn of residual elongation less than 60%, it is onlypossible to achieve a processing rate of, at most, 100 m/min, whereas inthe production method of the present invention processing rates of atleast 300 m/min are possible. More preferably, it is possible to carryout false-twisting at above 600 m/min and still more preferably at above800 m/min, and this is industrially advantageous.

In order to enhance the textured yarn high level transit properties, itis preferred that entangling be conferred with the aim of enhancing theyarn convergence. In FIG. 2, entangling is carried out using anentangling nozzle 8 while performing relaxation between the 3^(rd) FR 7and the 4^(th) FR 8. Methods for enhancing the convergence includetwisting and supplementary oiling, etc, and these may be used whererequired.

The Young's modulus of PPT fibre is low compared to that of polyethyleneterephthalate fibre, so the crimp is soft. However, in order to confer asense of tightness when formed into cloth, a suitable degree of hardnessis required and so textured yarn of deformed cross-section is preferred.In particular, when the cross-sectional shape of the PPT undrawn yarn isround such an effect is considerable, and it is possible to confer asuitable degree of flexural hardness by the sectional shape effect.However, if sectional deformation is produced to a marked extent,glitter and harshness are manifested, so the degree of sectionaldeformation is preferably 1.3-1.8. In order to achieve this, it ispreferred in particular that the yarn temperature at the false-twistedheater outlet be 100-175° C.

Furthermore, when the degree of sectional deformation is 1.3-1.7, asense of tightness is manifested and there is also little surfacereflection, so this is further preferred.

As stated above, the Young's modulus of PPT fibre is low and twistpropagation to the upstream twisting region is difficult. In order toimprove this, it is preferred that an oil agent or the like be appliedto the polypropylene terephthalate undrawn yarn, and that the contactresistance in terms of the heater, cooling plate and the guides, etc, belowered. When various types of oil agent component were applied to theundrawn yarn for this purpose and draw-texturing carried out, it wasdiscovered that smoothing agent components comprising water-insolublefatty acid esters and/or aromatic esters were effective. In particular,when 0.05 to 1.0 wt % thereof is applied in terms of the weight of theundrawn yarn, the frictional resistance in terms of the heater, coolingplate and guides is reduced, it is possible to propagate the twisteffectively to the upstream twisting region, and it is found that thereis little occurrence of fibrillation and little difference in dyeingbetween spindles or within a spindle. Consequently, it is preferred thatwater-insoluble fatty acid esters and/or aromatic esters have beenapplied as a smoothing agent component to the textured yarn followingdraw-texturing. Oil agents may also provide high level transitproperties following the texturing, and such cases too are included.

With regard to the water-insoluble fatty acid esters and/or aromaticesters referred to here, as preferred examples amongst conventionalsmoothing agents there are esters of monohydric alcohols and monobasicaliphatic carboxylic acids such as methyl oleate, isopropyl myristate,octyl palmitate, oleyl laurate and oleyl oleate, esters of monohydricalcohols and polybasic aliphatic carboxylic acids such as dioctylsebacate and dioleyl adipate, esters of monohydric alcohols and aromaticcarboxylic acids such as dioctyl phthalate and trioleeyl trimellitate,esters of polyhydric alcohols and monobasic aliphatic carboxylic acidssuch as ethylene glycol dioleate, trimethylol propane tricaprylate andglyceryl trioleate, and derivatives of such esters such as alkyleneoxide adduct esters like lauryl (EO) n-octanoate (it is preferred thatthe number of mols of added alkylene oxide be no more than 5 mols inthat, as the compound becomes more water soluble or self-dispersible inwater, so the smoothening properties are impaired), and these may beused on their own or in mixtures. However, there is no particularrestriction to these examples. If a mineral oil such as liquid paraffinor spindle oil is used on its own, the heat resistance is impaired, soin a preferred example these are used as a mixture not exceeding 40 wt %of the smoothing agent component. Again, the amount of smoothing agentincorporated is not restricted but it is preferably 50-70 wt % of theoil agent components.

It is also preferred that, as well as the smoothing agent, an emulsifierand other additives are included amongst the oil agent componentsapplied to the undrawn yarn.

Conventional emulsifiers can be used as the emulsifier component,suitable examples being nonionic surfactants such as the alkylene oxideadducts of compounds with one or more than one active hydrogen, such asthe alkylene oxide adducts of monohydric hydroxy compounds like laurylalcohol, isostearyl alcohol, oleyl alcohol, octylphenol and nonylphenol, polyhydric alcohol partial esters such as glyceryl monooleateester, sorbitan monolaurate ester and trimethylolpropane distearateester, and the alkylene oxide adducts thereof, alkylene oxide adducts ofcastor oil, the alkylene oxide adducts of alkylamines like laurylamineand stearylamine, the alkylene oxide adducts of higher fatty acids suchas myristic acid, stearic acid and oleic acid, and the alkylene oxideadducts of the amides derived from these fatty acids. Examples of thealkylene oxides here are ethylene oxide, propylene oxide and the like,on their own or used in the form of mixtures. Furthermore, there canalso be used, as emulsifiers, polyethylene glycol/polypropylene glycolblock copolymers, and anionic surfactants such as the aforesaid higherfatty salts and their triethanolamine or diethanolamine salts, etc, andTurkey red oil or the like. The amount of emulsifier incorporated is notrestricted but it is preferably 20-50 wt % of the oily agent components.

Furthermore, besides additives employed in accordance with propertiesrequired in the spinning and draw texturing, such as antistatic agentslike alkylsulphonate alkali metal salts, alkylphosphate alkali metalsalts, polyalkylene glycol alkylphosphate alkali metal salts, fatty acidsoaps, alkylimidazolines and the like, there may be used at the sametime additives such as conventional converging agents, rust preventives,preservatives, antioxidants and the like. The amount of such additivesincluded is not particularly restricted but it is preferably from 5 to15 wt %, so that the smoothening properties and heat resistance are notimpaired.

Moreover, as a method for determining whether water-insoluble fatty acidester and/or aromatic ester has been applied to the textured yarn, theoil agent components may be extracted by a methanol extraction method,and determination then performed from the peak positions in the IRspectrum of the extracted components.

There are no restrictions on the PPT textured yarn fineness, thefineness of the individual filaments, and the cross-sectional shape,etc, but normally a multifilament yarn of 33 to 560 dtex and filamentfineness 0.11 to 11 dtex is preferably used, and the cross-sectionalshape may be round shaped, flat, polygonal such as triagonal,multi-lobed such as trilobal, or hollow, and suitable selection is madeaccording to the application objectives. Furthermore, a multifilament ispreferably composed of individual filaments of different fineness and/orcross-sectional shape.

Known textured yarn produced by the spindle texturing of PPT drawn yarnis excellent in its stretchability and bulkiness but there is theproblem that there are often dyeing differences between spindles orwithin a spindle. The main reason for this is because the Young'smodulus of PPT drawn yarn is low, so there is poor twist propagationand, furthermore, since the twist tension is low at less than 0.17cN/dtex the twisting range within the heater varies between spindles andwithin a spindle. In contrast, with the PPT textured yarn obtained bythe method of the present invention, there is little difference indyeing between spindles and within a spindle, and there is littlefibrillation, so textured yarn of high product quality is formed.

EXAMPLES

Below, the present invention is explained in further detail by means ofexamples. Now, in the examples the properties were determined by thefollowing methods.

A. Intrinsic Viscosity

This was obtained using o-chlorophenol solutions of the sample, with therelative viscosity at 25° C. being determined at various points by meansof an Ostwald viscometer, and then extrapolation performed to zeroconcentration.

B. Strength/Elongation

These were measured for the undrawn yarn under the constant rate ofextension conditions as described in JIS L1013 (Test Methods forMan-Made Filament Yarns) using a Tensilon UCT-100 made by the OrientecCo. The elongation at break was determined from the elongation at thepoint of maximum tenacity on the stress-strain curve.

C. Birefringence

The retardation Γ and the optical path length d were measured for theundrawn yam using a BH-2 polarizing microscope made by the Olympus Co.,and the birefringence was determined from the relationship Δn=Γ/d.

D. Boiling Water Shrinkage

Measurement was carried out based on JIS L 1013 (Test Methods forMan-Made Filament Yarns). From the undrawn yarn package, a hank wastaken using a counter wheel, and the hank length L₁ measured with alength measurement load of 90×10⁻³ cN/dtex applied. Then this lengthmeasurement load was removed and the hank introduced into boiling waterfor 15 minutes, after which it was removed, air dried, the lengthmeasurement load again applied and hank length L₂ measured. The boilingwater shrinkage was calculated using the following formula.

boiling water shrinkage (%)=[(L ₁ −L ₂)/L ₁]×100

E. Uster Unevenness

The yarn lengthwise direction thickness unevenness (normal test) wasmeasured using an Uster Tester Monitor C made by the Zellweger-Uster Co.The conditions were a yarn supply rate of 50 m/min for 1 minute, and themean deviation (U%) was measured in normal mode.

F. Saddle and Bulging

As shown in FIG. 6, the wound thickness L₁ in the centre region of theundrawn yarn package and the wound thickness at the end face L₂ weremeasured, and the value of L₂ minur L₁ was taken as the magnitude of thesaddle. Furthermore, the wound width L₃ of the innermost layer in theundrawn yarn package as shown in FIG. 6 and L₄ which denotes thegreatest wound width were measured, and the percentage bulgingcalculated by means of the following formula.

bulging(%)=(L ₄ −L ₃)/L ₃×100

G. Measurement of the Yarn Temperature at the Heater Outlet

The yarn temperature was measured right after the heater outlet using aninstrument sold by Tokyo Seiko Co. Ltd, power source region: TS-3A,detector end: EC-2.

H. Yarn Tension

This was measured using a digital tension meter IT-200 produced byIntec.

I. Number of Twists within Heater

The line was simultaneously grasped at the heater inlet and outletregions during the false-twisting process and the yarn within the heatersampled. Then, using a motor-operated twist detector, the number oftwists T (T/m) was measured under a 90×10⁻³ cN/dtex load.

J. Degree of Sectional Deformation

The yarn was cut perpendicular to the yarn lengthwise direction and aslice taken. A micrograph of the cross-section was recorded using anoptical microscope. From the micrograph of the cross-section, there wasobtained for each single fibre the value of the ratio of the diameter ofthe circumscribed circle to the diameter of the inscribed circle,divided by the ratio of the diameter of circumscribed circle to thediameter of the inscribed circle in the case of the yarn supplied to thefalse-twisting process, and the average value calculated.

K. Percentage Recovery of Shrinkage: RS

Textured yarn which had been left for 1 week on the package was sampled,and a small hank produced in accordance with JIS L1090-1992, 5.8Percentage Shrinkage Recovery. After leaving to contract for 24 hours,it was immersed for 30 minutes in hot water at 98° C. wrapped withcoarse cloth. Thereafter, the sample was withdrawn and allowed to drynaturally for 24 hours on filter paper, and then the sample measured inaccordance with 5.8 Percentage Shrinkage Recovery.

L. Knitting Inspection

The outermost surface of a textured yarn cheese was removed and, using acircular knitting machine of suitable gauge number, after adjusting thedensity, circular knitting was carried out in turn such that there wereadjacent levels for comparison. Based on the knitted material weight,0.3% (owf) of Sumikaron Navy Blue S-2GL 200 (produced by the SumitomoChemical Co.), 5.0% (owf) of Tetrosin PEC (produced by Yamakawa ChemicalIndustry Co.) and 1.0% Nicca Sansolt #1200 (produced by Nikka ChemicalCo.) were uniformly dispersed in 50 times the quantity of water asweight of knitted material. After adjusting to 50° C., the knittedmaterial was introduced and, while suitably stirring, the temperaturewas raised to 98° C. at 1-2° C. per minute, followed by 20 minutesheating, after which slow cooling was performed and the sample dyed.With regard to the knitting inspection, the L value of the knittedmaterial was measured using a calorimeter. When the average value forall was within ±0.4, the sample was regarded as having passed the text.Samples lying outside this range failed the test.

Example 1

PPT of intrinsic viscosity [η] 0.89 was spun by means of the spinningmachine shown in FIG. 3 at a spinning temperature of 260° C. using aspinneret with 36 holes of round shape, and highly-oriented undrawn yarnwas wound-up over 2 hours at a spinning rate of 3000 m/min. At the timeof wind-up, using an oiling guide, the undrawn yarn was oiled with anoil agent in which a smoothing agent, emulsifier and additives had beendispersed, and there was applied 0.2 wt % of oleyl laurate in terms ofthe weight of the undrawn yarn. The properties of the undrawn yarn areshown in Table 1. The measurement of the properties was carried outimmediately after winding-up. Following wind-up, the highly orientedundrawn yarn was directly subjected to draw texturing under theconditions in Table 2 using the false-twisting machine shown in FIG. 2.Now, as heater 3, there was used a 2.5 m dry-heat heater, and asfrictional false-twisting device 5 there was employed a triaxial twisterconstructed of, from the upstream side, one ceramic disc, six urethanediscs and one ceramic disc. Again, compared to the 2^(nd) FR 6, thevelocity of the 3^(rd) FR 7 was 18% slower and no entangling nozzle 8was used. The false-twisting could be carried out stably and it waspossible to obtain a bulky textured yarn. The textured yarn propertiesare shown in Table 3. The textured yarn was subjected to circularknitting using a 27G circular knitting machine and when a knittinginspection was carried out, no dyeing differences were noted between theinner and outer layers of the undrawn yarn package.

Comparative Example 1

PPT of intrinsic viscosity [η] 0.89 was spun by means of the spinningmachine shown in FIG. 3 at a spinning temperature of 260° C. using aspinneret with 36 holes of round shape, and undrawn yarn was wound-up ata spinning rate of 1500 m/min.

After winding-up for 5 hours, the yarn was left for 1 week in a room at25° C. and 80% relative humidity. The package of undrawn polypropyleneterephthalate yarn exhibited package tightening, the centre region waslarge compared to the end face and a depressed shape was formed. Theproperties of the undrawn yarn after leaving for 1 week are shown inTable 1. Using identical equipment to that in Example 1, draw texturingwas carried out under the conditions shown in Table 2. Thefalse-twisting process was rather unstable and there were many yarnbreaks. The properties of the textured yarn are shown in Table 3. Thetextured yarn was subjected to circular knitting using a 27G circularknitting machine and when a knitting inspection was carried out, amarked difference in dyeing was noted between the inner and outer layersof the undrawn yarn package and unevenness coinciding with the edge faceperiod was observed, so there were problems in terms of product quality.

Comparative Example 2

PPT of intrinsic viscosity [η] 0.89 was spun by means of the spinningmachine shown in FIG. 3 at a spinning temperature of 260° C. using aspinneret with 36 holes of round shape, and undrawn yarn was wound-up ata spinning rate of 2000 m/min.

After winding-up for 5 hours, the yarn was left for 1 week in a room at25° C. and 80% relative humidity. The package of undrawn polypropyleneterephthalate yarn exhibited package tightening, the centre region waslarge compared to the end face and a depressed shape was formed. Theproperties of the undrawn yarn after leaving for 1 week are shown inTable 1. Using identical equipment to that in Example 1, draw texturingwas carried out under the conditions shown in Table 2. Thefalse-twisting process was rather unstable and there were many yarnbreaks. The properties of the textured yarn are shown in Table 3. Thetextured yarn was subjected to circular knitting using a 27G circularknitting machine and when a knitting inspection was carried out, amarked difference in dyeing was noted between the inner and outer layersof the undrawn yarn package and unevenness coinciding with the edge faceperiod was observed, so there were problems in terms of product quality.

Comparative Example 3

PPT of intrinsic viscosity [η] 0.89 was spun at a spinning temperatureof 260° C. using a spinneret with 36 holes of round shape, and undrawnyarn wound-up at a spinning rate of 1200 m/min. Next, drawing wascarried out at a drawing rate of 600 m/min, at a 1^(st) hot rolltemperature of 60° C., a draw ratio of 3 and a 2^(nd) hot rolltemperature of 140° C., after which the yarn was wound-up using aspindle wind-up device and 56 dtex/36f drawn yarn obtained. Using thisdrawn yarn, false-twisting was carried out under the conditions in Table2 employing a 1 m dry-heat heater and a spindle false-twisting device.The spindle rotation rate was set to 4100 rpm. When 100 kg of texturingwas continuously carried out, to produce 100 units of 1 kg woundtextured yarn, despite the processing rate being low at 100 m/min, thepercentage of yarn breaks reached 5% and, furthermore, the pass rate inthe textured yarn knitting inspection was only 92%.

Examples 2 to 4

PPT of intrinsic viscosity [η] 0.89 was spun by means of the spinningmachine shown in FIG. 4 at a spinning temperature of 260° C. using aspinneret with 36 holes of round shape, and while haulint-off at a rateof 3000 m/min a dry heat treatment was carried out with two godet rollsheated to 110° C. after which the undrawn yarn was wound- up. At thattime, using an oiling guide the undrawn yarn was oiled with an oil agentin which a smoothing agent, emulsifier and additives had been dispersedand there was applied 0.2 wt % of oleyl laurate in terms of the weightof the undrawn yarn.

The yarn was left for 1 week under the same conditions as in ComparativeExample 1, but no tightening on the undrawn yarn package was produced.After leaving for 1 week, the properties of the undrawn yarn were asshown in Table 1. Using this undrawn yarn, draw texturing was carriedout with the same device and under the same processing conditions as inExample 1, except that the heater temperature was as shown in Table 2.The false-twisting could be carried out stably and it was possible toobtain a bulky textured yarn. The textured yarn was subjected tocircular knitting using a 27G circular knitting machine and when aknitting inspection was carried out, no dyeing differences were notedbetween the inner and outer layers of the undrawn yarn package.Furthermore, as the false-twisting temperature became higher, so thecrimp became stronger and the yarn bulkier, and the degree of sectionaldeformation became greater, so the flexural hardness of the filamentsincreased and there was a suitable tightness of feel.

Comparative Examples 4 and 5

Using the same kind of undrawn yarn as in Examples 2 to 4, drawtexturing was carried out under the conditions shown in Table 2. Thefalse-twisting device was the same as in Example 1 and, excepting forthe draw ratio, the draw texturing was carried out under the sameconditions as in Example 3. However, in Comparative Example 4,ballooning was produced in the twisting zone and the unwinding tensionfluctuated, so processing was unstable. On the other hand, inComparative Example 5, yarn breakage occurred during start-up and it wasnot possible to obtain textured yarn. The draw-textured yarn propertiesin the case of Comparative Example 4 are shown in Table 3. The texturedyarn was subjected to circular knitting using a 27G circular knittingmachine and when a knitting inspection was carried out, dyeingunevenness was noted in the yarn lengthwise direction and there wereproblems in terms of product quality.

Example 5

Using the same kind of undrawn yarn as in Examples 2 to 4, drawtexturing was carried out under the conditions shown in Table 2. As thefalse-twisting device, there was employed a TFT-15 made by the TorayEngineering Co. (using a 1 m non-contact type high temperature heater asthe heater). Furthermore, the velocity of the 3^(rd) FR 7 was slowed 15%compared to the 2^(nd) FR 6, and no entangling was conferred. When therewas continuously carried out the draw texturing of 500 kg of undrawnyarn and 100 units of 5 kg wound yarn were produced, it was possible toproduce high quality textured yarn with a percentage of yarn breaks of1% and a pass rate in the knitting inspection of 98%.

Examples 6 and 7

PPT of intrinsic viscosity [η] 0.89 was spun by means of the spinningmachine shown in FIG. 5 at a spinning temperature of 260° C. using aspinneret 26 with 36 holes of round shape and, after cooling the yarn inchimney 27 to below the Tg, a heat treatment was carried out with anon-contact heater 28 (heating length: 1.5 m, heating medium: air heatedto 180° C. ) positioned 1.6 m below the spinneret and undrawn yarn waswound up at a rate of 3500 m/min. At the time of wind-up, using oilingdevice 29 the undrawn yarn was oiled with an oil agent in which asmoothing agent, emulsifier and additives had been dispersed and therewas applied 0.2 wt % of oleyl laurate in terms of the weight of theundrawn yarn. The yarn was left for 1 week under the same conditions asin Comparative Example 1, but no tightening of the undrawn yarn packagewas produced. After leaving for 1 week, the properties of the undrawnyarn were as shown in Table 1. Using this undrawn yarn, draw texturingwas carried out with the same device as in Example 1, using theprocessing conditions shown in Table 2. The false-twisting could becarried out stably and it was possible to obtain a bulky textured yarn.The textured yarn was subjected to circular knitting using a 27Gcircular knitting machine and when a knitting inspection was carriedout, no dyeing differences were noted between the inner and outer layersof the undrawn yarn package, or corresponding to the edge face period.

Example 8

PPT of intrinsic viscosity [η] 0.89 was spun by means of the spinningmachine shown in FIG. 4 at a spinning temperature of 260° C. using aspinneret with 36 holes of round shape and while hauling-off at a rateof 2600 m/min a dry heat treatment was carried out with the two godetrolls heated to 110° C. after which the undrawn yarn was wound-up. Atthe time of wind-up, using an oiling guide the undrawn yarn was oiledwith an oil agent in which a smoothing agent, emulsifier and additiveshad been dispersed and there was applied 0.2 wt % of oleyl laurate interms of the weight of the undrawn yarn. The yarn was left for 1 weekunder the same conditions as in Comparative Example 1, but no tighteningon the undrawn yarn package was produced. After leaving for 1 week, theproperties of the undrawn yarn were as shown in Table 1. Using thisundrawn yarn, draw texturing was carried out with the same device as inExample 1, employing processing conditions as shown in Table 2, and itwas possible to obtain a bulky textured yarn. The textured yarn wassubjected to circular knitting using a 27G circular knitting machine andwhen a knitting inspection was carried out, no dyeing differences werenoted between the inner and outer layers of the undrawn yarn package.

Effects of the Invention

In accordance with the present invention, it is possible to produce, atlow cost, polypropylene terephthalate textured yarn with little dyeingunevenness or fibrillation, and which is outstanding in its productquality. Not only is this textured yarn excellent in its stretchabilityand bulkiness, but it forms fabric having a suitable sense of tightness.

TABLE 1 Boiling Spinning Strength Elongation Water Uster Bulging 0.585 ×0.75 × Rate ST Birefringence EL Shrinkage Unevenness Saddle Factor (1 +(1 + (m/min) (cN/dtex) (×10⁻³) (%) (%) (U%) (mm) (%) EL/100) EL/100)Example 1 3000 2.6 52.5 119 40 1.22 4.2 5 1.28 1.64 Comp. Ex. 1 1500 1.423.1 300 52 1.98 5.5 11  — — Comp. Ex. 2 2000 1.8 34.9 195 56 1.43 4.4 71.73 2.21 Examples 2 to 5 3000 2.5 43.8 98.5 6.6 0.98 2.5 5 1.16 1.49Comp. Ex 4 and 5 Examples 6 and 7 3500 3.1 57.8 76.5 9.0 0.60 2.0 4 1.031.32 Example 8 2600 2.0 43.7 158 6.0 0.96 1.8 4 1.51 1.93

TABLE 2 Processing Rate Draw Ratio Yarn Temp. at T₁ False Twist No.(m/min) DR Heater Outlet (° C.) (cN/dtex) T₁/T_(H) T(×D^(½)) Example 1300 1.4 150 0.35 1.18 28400 Example 2 300 1.4 100 0.36 1.24 27900Example 3 300 1.4 150 0.35 1.18 28400 Example 4 300 1.4 175 0.34 1.1528700 Example 5 600 1.4 150 0.34 1.15 28800 Comparative Ex. 1 100 2.67100 0.37 1.32 27200 Comparative Ex. 2 100 2.0 100 0.37 1.31 27600Comparative Ex. 3 100 1.03 150 0.13 1.25 30400 Comparative Ex. 4 3001.15 150 0.23 1.32 27100 Comparative Ex. 5 300 1.55 150 — — — Example 6300 1.05 130 0.18 1.03 28700 Example 7 300 1.10 150 0.25 1.11 28800Example 8 300 1.65 150 0.35 1.16 28500

TABLE 3 Fineness Strength ST Elongation EL RS Degree Of SectionalBoiling Water (dtex) (cN/dtex) (%) (%) Deformation Shrinkage SW (%)Example 1 58 2.9 36 45 1.5 9 Example 2 58 2.7 36 42 1.4 11  Example 3 582.9 38 45 1.5 9 Example 4 58 3.0 33 45 1.8 8 Example 5 58 3.0 38 48 1.69 Comparative Ex. 1 56 2.5 38 40 1.6 9 Comparative Ex. 2 56 2.7 37 401.6 9 Comparative Ex. 3 53 2.8 35 48 1.1 9 Comparative Ex. 4 70 2.6 6432 1.3 9 Example 6 98 2.8 50 43 1.2 9 Example 7 103  2.9 43 44 1.3 10 Example 8 59 2.8 41 45 1.6 9

What is claimed is:
 1. A method of producing polypropylene terephthalatetextured yarn which is characterized in that, when carrying outtexturing at the same time as drawing using a frictional false-twistingmachine, at the same time as setting the draw ratio of the polypropyleneterephthalate undrawn yarn to a draw ratio in the range 1.05 to 1.70,the elongation EL (%) of the undrawn yarn and the draw ratio DR are setso that the following relationship (1) is satisfied0.585×(1+EL/100)≦DR≦0.75×(1+EL/100)  Relationship (1).
 2. A method ofproducing polypropylene terephthalate textured yarn according to claim 1which is characterized in that the draw ratio is from 1.05 to 1.60.
 3. Amethod of producing polypropylene terephthalate textured yarn accordingto claim 2 which is characterized in that the draw ratio is from 1.10 to1.50.
 4. A method of producing polypropylene terephthalate textured yarnaccording to claim 1 which is characterized in that the yarn temperatureat the texturing heater outlet is from 30 to 175° C.
 5. A method ofproducing polypropylene terephthalate textured yarn according to claim 1which is characterized in that the yarn temperature at the texturingheater outlet is from 110 to 160° C.
 6. A method of producingpolypropylene terephthalate textured yarn according to claim 1 which ischaracterized in that the texturing tension T₁ is from 0.17 to 0.55cN/dtex.
 7. A method of producing polypropylene terephthalate texturedyarn according to claim 1 which is characterized in that the ratioT₁/T_(H) of the texturing tension T₁ to the tension in front of theheater T_(H) is from 1.02 to 1.30.
 8. A method of producingpolypropylene terephthalate textured yarn according to claim 1 which ischaracterized in that the number of twists T inside the heater is from27400/D^(½) to 30600/D^(½).
 9. A method of producing polypropyleneterephthalate textured yarn according to claim 1 which is characterizedin that a non-contact type heater is used as the heater.
 10. A method ofproducing polypropylene terephthalate textured yarn according to claim 1which is characterized in that there is used polypropylene terephthalateundrawn yarn which satisfies the following relationships (1) to (4); (1)strength ST (cN/dtex): 1.8≦ST (2) birefringence Δn (×10⁻³): 30≦Δn≦70 (3)elongation EL (%): 60≦EL≦180 (4) boiling water shrinkage SW (%):3≦SW≦15.
 11. A method of producing polypropylene terephthalate texturedyarn according to claim 10 which is characterized in that the yarnthickness variation U % (normal mode) of no more than 1% is used as theundrawn yarn.
 12. A method of producing polypropylene terephthalatetextured yarn according to claim 10 which is characterized in that thereis used an undrawn yarn package of saddle less than 4 mm and bulgingfactor less than 10%.
 13. A method of producing polypropyleneterephthalate textured yarn according to claim 10 which is characterizedin that there is used, as the supplied raw yarn, undrawn yarn obtainedby melt spinning polyester in which polypropylene terephthalate is thechief component and then cooling and solidifying the spun yarn, afterwhich the yarn is hauled-off at a spinning rate of 2500-4500 m/min and,furthermore, heat-treated for a heat-treatment time of at least 0.01second and wound up.
 14. A method of producing polypropyleneterephthalate textured yarn according to claim 13 which is characterizedin that, as the supplied raw yarn, there is used undrawn yarn obtainedby carrying out the heat-treatment at a temperature in the range 70 to130° C. employing a contact type heater, and then winding up.
 15. Amethod of producing polypropylene terephthalate textured yarn accordingto claim 13 which is characterized in that, as the supplied raw yarn,there is used undrawn yarn obtained by carrying out the heat-treatmentat a temperature in the range 120 to 220° C. employing a non-contacttype heater, and then winding up.
 16. A method of producingpolypropylene terephthalate textured yarn according to claim 1 which ischaracterized in that after the draw texturing, up to the winding-up,there is provided a relaxation zone where the relaxation factor is 5 to25%.
 17. A method of producing polypropylene terephthalate textured yarnaccording to claim 1 which is characterized in that the draw texturingprocessing rate is at least 300 m/min.
 18. Polypropylene terephthalatetextured yarn which is characterized in that it is produced by a methodaccording to any of claim
 1. 19. Polypropylene terephthalate texturedyarn according to claim 18 which is characterized in that the degree ofcross-sectional deformation is 1.3 to 1.8.
 20. Polypropyleneterephthalate textured yarn according to claim 18 which is characterizedin that there has been applied as a smoothing agent component awater-insoluble aliphatic ester and/or aromatic ester.